The present invention relates to an apparatus for detecting an insulation defect in at least one device connected into an electrical power transmission or distribution network and provided with an earthing ground line. It also concerns a detection process implemented within such an apparatus.
The detection apparatuses of this type, known in the state of the art, include means of measuring a leakage current travelling down the said earthing line and liable to contain at least one discharge internal to the said device and engendered in the presence of an insulation defect, these means being arranged on the earthing line of each device, a unit for capture of the measurement signal delivered by the measuring means including means of analogue/digital conversion of the said measurement signal, and a signal processing unit linked to the capture unit and including means of comparing a digital signal resulting from the said conversion with a maximum threshold value representative of the maximum value of the leakage current permitted to flow in the said earthing line, with a view to obtaining, from this comparison, an insulation defect signal.
Such detection apparatuses allow the monitoring of devices by analysis of partial discharges and thus ensure the detection of any aging of the internal insulation of the devices.
These apparatuses are especially adapted to the monitoring of current or voltage transformers of electrical power transmission or distribution networks.
However, the apparatuses of this type have numerous drawbacks, especially by virtue of the fact that they are not capable of effectively distinguishing between the discharges engendered by the network in particular by the corona effect and the discharges engendered in the presence of an insulation defect. They are therefore liable to generate false alarms.